The configuration of an electroluminescent (hereinafter, may be abbreviated to EL) element is based on a laminated structure in which a light emitting layer and optional layers having other functions are laminated between a pair of electrodes.
EL elements have low resistance to moisture, and shrink, a dark spot and the like occur in the elements under the effect of moisture. Here, the term “shrink” means a phenomenon in which, as time elapses, the expansion of non-light emitting regions proceeds as if the light emitting region shrinks away. Also, the term “dark spot” means a non-light emitting region such as a black spot that occurs immediately after the production of an EL element. This dark spot also occasionally expands along with a lapse of time. In other words, EL elements deteriorate over time due to the presence of moisture.
Among the techniques for preventing the penetration of moisture into EL elements, encapsulation of EL elements by means of a sealing member or a sealing structure constitutes the mainstream, and investigations on various techniques have been conducted hitherto.
Furthermore, since EL elements have light emission efficiency that does not reach 100%, a portion of the energy generated as a result of recombination is converted to heat. Furthermore, the heat generated as a loss at the time of light emission is essentially likely to remain inside the EL elements. However, EL elements are generally vulnerable to heat. For this reason, if heat is retained inside an EL element for a long time or a large amount of heat is retained, there is a risk that there may occur luminescence unevenness, shortening of the service life due to heat, and at the worst, destruction of the EL element itself. Particularly, in the case of EL elements for illumination purposes, such occurrences pose a serious problem. Also, if the amount of heat is large, gas may be generated from the members constituting an element, and there is a risk that the element may be deteriorated by this outgas generated inside the element.
In order to address this problem, investigations have been conducted to impart heat dissipation properties to sealing members or sealing structures, and for example, there have been suggested a sealing member in which at least one surface of a metal plate having predetermined heat conductivity is covered with an insulating layer (see, for example, Patent Literature 1); and sealing structures in which a heat absorbent that absorbs the heat generated in EL elements, and a heat dissipater that dissipates the absorbed heat to the outside are laminated in sequence on a metal plate or a metal foil (see, for example, Patent Literatures 2 to 4). Furthermore, investigations are also being conducted to impart heat dissipation properties not to the sealing members or sealing structures, but to the substrate that supports EL elements (see, for example, Patent Literature 5).
Meanwhile, such a problem that prevention of the penetration of moisture and provision of a heat dissipation function are needed, is not limited only to EL elements. That is, the problem is not limited to elements that convert electricity to light, but commonly occurs also in elements that convert light to electricity, such as organic thin-film solar cell and solid-state sensors.